Questions: Girl's Behavior

I have a lot of nasty and hurtful things I think for some reason, it could stem from constant rejection and feeling hated.. I don't know.. but I know I should restrict myself from saying these offensive things and be nice to people even if I do have these nasty thought... So that I will be liked... But then again I think that's being fake and I try to be true as possible, so I usually let all these unfiltered nasty thoughts jus spew out all over the internet, and a lot of people seem to hate me and insult me for it... I don't know if I'm doing it wrong, maybe I should hold back from saying this offensive stuff I think?

Also, does anyone else have these natural / nasty thoughts but hold them back?
Or am I not normal and most people naturally think nice things at all times?

I asked a while ago about if I misread things with this girl at an ice cream store. She would always talk to me about music and podcasts cause I started a conversation the first time I saw her. I went in a few times, she was excited to see me and we'd talk a bit. Even to where her coworker would give her a funny look.
Last time I went there, I mentioned I had been moving and she was concerned I was moving out of state, but she said she was happy I was staying local. So before I left I asked if I could give her my number for the podcasts 😉

She said she had a boyfriend. So I was apologetic and left.

It's been a few weeks, and I saw her today. She wasn't as warm as first but we still talked, she asked what kind of schedule do I work, how my day was going and she told me about hers. When I was paying with her, I apologized for the last time, and she was very sweet and said it was all good and I left. I said I did enjoy talking to her as I turned to leave.

But I was really confused, I figured there was flirting and possibly an attraction because how she was worried I wasn't gonna come by.

Even though she has a boyfriend, does she maybe like me in some way? Or just enjoying talking to me?